1. Field of the Invention
This invention relates to a fuel injection control system and method and an engine control unit for an internal combustion engine having two types of variable valve mechanisms each of which changes the cam phase and the cam profile of at least one of each intake cam and each exhaust cam for opening and closing respective intake and exhaust valves.
2. Description of the Prior Art
Conventionally, a fuel injection control system for an internal combustion engine has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 11-301144, which includes a variable valve mechanism. The variable valve mechanism of the proposed fuel injection control system changes the phase angle of intake cam (hereinafter referred to as xe2x80x9cthe cam phasexe2x80x9d) of each intake cam with respect to a crankshaft, whereby the valve timing of the intake valve, i.e. the valve overlap of the intake valve and an associated exhaust valve is changed to change charging efficiency of the engine. Further, the fuel injection control system determines the charging efficiency by searching a map based on a rotational speed of the engine and boost pressure (differential pressure between the intake pipe pressure and atmospheric pressure) and an actual cam phase, and determines the amount of intake air based on the charging efficiency and the intake pipe pressure. Further, the injection control system determines the fuel injection amount (i.e. amount of fuel to be injected into the cylinder) based on the amount of intake air, and causes the fuel injection to be carried out based on the fuel injection amount thus determined.
Further, another fuel injection control system for an internal combustion engine has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 3-3901, which includes another type of variable valve mechanism. This engine has intake cams and exhaust cams, each of which is comprised of a low-speed cam and a high-speed cam having a higher cam profile than a cam profile of the low-speed cam. This variable valve mechanism switches each cam between the low-speed cam and the high-speed cam to change the valve lift amount of the intake valve and the exhaust valve to thereby change the charging efficiency. Further, the fuel injection control system searches respective maps associated with the low-speed cam and the high-speed cam based on the rotational speed of the engine and the intake pipe pressure, to thereby determine the fuel injection amount suitable for the high-speed cam or for the low-speed cam, and causes the fuel injection to be carried out based on the fuel injection amount thus determined.
Conventionally, it has been desired to reduce exhaust emissions and enhance engine output, and from this point of view, it is contemplated that a single internal combustion engine incorporates the two types of variable valve mechanisms described above. When the engine is configured to incorporate the two types of variable valve mechanisms, they exert influences upon each other to change the charging efficiency. However, in both of the former and latter fuel injection control systems, the fuel injection amount is calculated based on the charging efficiency based on only one of the two types of variable valve mechanisms, and hence the control system incorporating them cannot calculate the fuel injection amount as a value suited to the charging efficiency at the time, so that the fuel injection control cannot be performed properly, causing e.g. degraded drivability and increased exhaust emissions. Further, a combination of the above two fuel injection control systems would require a large number of maps of preset values to determine the fuel injection amount, and the calculating process becomes complicated.
It is an object of the invention to provide a fuel injection control system and method and an engine control unit for an internal combustion engine including two types of variable valve mechanisms capable of changing a camp phase and a cam profile, respectively, which are capable of determining an amount of fuel to be injected as a value suited to charging efficiency at the time by simplified calculation processing, thereby performing the fuel injection control properly in a simplified manner.
To attain the above object, according to a first aspect of the invention, there is provided a fuel injection control system for an internal combustion engine including intake cams and exhaust cams for opening and closing respective intake valves and exhaust valves, wherein a cam phase as a phase of at least one of each intake cam and each exhaust cam relative to a crankshaft is changeable, and at least one of the intake cam and the exhaust cam can be switched to one of a plurality of kinds of cams having respective profiles different from each other.
The fuel injection control system according to the first aspect of the invention is characterized by comprising:
an engine rotational speed-detecting module for detecting a rotational speed of the engine;
a cam phase-detecting module for detecting the cam phase;
an intake pipe pressure parameter-determining module for determining an intake pipe pressure parameter representative of an intake pipe pressure;
a first parameter-determining module for determining a first parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase;
a second parameter-determining module for determining a second parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase; and
a fuel injection amount-calculating module for calculating an amount of fuel to be injected, by using a linear equation of the intake pipe pressure parameter, the linear equation having a slope of the first parameter and an intercept of the second parameter.
In this engine, each intake cam and/or each exhaust cam has a cam phase thereof changed to thereby change the valve timing, and is switched to one of a plurality of kinds of cams having respective cam profiles different from each other to thereby change the amount of valve lift. Further, according to the fuel injection control system for the engine, the intake pipe pressure parameter representative of the intake pipe pressure is determined, and the first and second parameters are determined in dependence on the one of the plurality of kinds of cam phases to which the intake cam and/or the exhaust cam is/are switched, and the detected rotational speed of the engine and the detected cam phase. Then, the amount of fuel to be injected is calculated based on the intake pipe pressure and the first and second parameters. Therefore, the amount of fuel to be injected can be calculated as a value suited to the charging efficiency obtained based on the valve timing and the amount of valve lift at the time. This enables appropriate execution of the fuel injection control. Further, since the fuel injection amount is calculated by the linear equation by using the above parameters, it is possible to calculate the fuel injection amount in a simplified manner without carrying out complicated calculating operations.
To attain the above object, according to a second aspect of the invention, there is provided a fuel injection control method for an internal combustion engine including intake cams and exhaust cams for opening and closing respective intake valves and exhaust valves, wherein a cam phase as a phase of at least one of each intake cam and each exhaust cam relative to a crankshaft is changeable, and at least one of the intake cam and the exhaust cam can be switched to one of a plurality of kinds of cams having respective profiles different from each other.
The fuel injection control method according to the second aspect of the invention is characterized by comprising the steps of:
detecting a rotational speed of said engine;
detecting the cam phase;
determining an intake pipe pressure parameter representative of an intake pipe pressure;
determining a first parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase;
determining a second parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase; and
calculating an amount of fuel to be injected, by using a linear equation of the intake pipe pressure parameter, the linear equation having a slope of the first parameter and an intercept of the second parameter.
This fuel injection control method provides the same advantageous effects as described above concerning the fuel injection control system according to the first aspect of the invention.
To attain the above object, according to a third aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out fuel injection control of an internal combustion engine including intake cams and exhaust cams for opening and closing respective intake valves and exhaust valves, wherein a cam phase as a phase of at least one of each intake cam and each exhaust cam relative to a crankshaft is changeable, and at least one of the intake cam and the exhaust cam can be switched to one of a plurality of kinds of cams having respective profiles different from each other.
The engine control unit according to the third aspect of the invention is characterized in that the control program causes the computer to detect a rotational speed of said engine, detect the cam phase, determine an intake pipe pressure parameter representative of an intake pipe pressure, determine a first parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase, determine a second parameter in dependence on the one of the plurality of cams to which the at least one of the intake cam and the exhaust cam is switched, the detected rotational speed of the engine, and the detected cam phase, and calculate an amount of fuel to be injected, by using a linear equation of the intake pipe pressure parameter, the linear equation having a slope of the first parameter and an intercept of the second parameter.
This engine control unit provides the same advantageous effects as described above concerning the fuel injection control system according to the first aspect of the invention.
Preferably, the first parameter is set to a larger value as the detected rotational speed of the engine is higher and the detected cam phase is more retarded.
Preferably, the second parameter is set to a larger value as the detected rotational speed of the engine is higher and the detected cam phase is more retarded.
Preferably, the plurality of kinds of cams have a higher cam profile and a lower cam profiles as the cam profiles, and the first parameter is set to a larger value when the at least one of the intake cam and the exhaust cam is switched to a cam having the higher cam profile than when the at least one of the intake cam and the exhaust cam is switched to a cam having the lower cam lower profile.
Preferably, the plurality of kinds of cams have a higher cam profile and a lower cam profiles as the cam profiles, and the second parameter is set to a larger value when the at least one of the intake cam and the exhaust cam is switched to a cam having the higher cam profile than when the at least one of the intake cam and the exhaust cam is switched to a cam having the lower cam lower profile.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.